How much heat is evolved when 1260 g of water condenses to a liquid at 100.°C?

To solve this you need the value for ΔHvap for water, which is a constant that tells you how much energy is used/released when water changes it's physical state from vapour to liquid, or liquid to vapor.

Moles H2O = 1233 g / 18 g/mol=68.5 68.5 x 40.7 = 2788 kJ